1. Field of the Invention
The present invention relates to a polishing apparatus and a polishing method, and more particularly to a polishing apparatus and a polishing method for polishing a surface of a substrate such as a semiconductor wafer to planarize the surface of the substrate.
2. Description of the Related Art
A polishing apparatus for polishing a surface of a substrate such as a semiconductor wafer generally has a loading/unloading section, a polishing section, and a cleaning section. The polishing section includes a polishing unit that has a polishing table having a polishing surface comprising a polishing pad, and a top ring (polishing head) for holding the substrate. In the polishing unit, while the substrate held by the top ring is pressed against the polishing surface of the polishing pad under a certain pressure, the polishing table and the top ring are moved relative to each other to bring the substrate in sliding contact with the polishing surface, thereby polishing the surface of the substrate to a flat mirror finish. In the polishing unit which performs chemical mechanical polishing (CMP), a polishing liquid (slurry) is supplied to the polishing surface from a polishing liquid supply nozzle during polishing of the substrate. Therefore, after the substrate is polished, polishing residues (particles) such as a polishing liquid, polishing debris and the like remain on the surface of the substrate and a substrate holding surface of the top ring.
In order to remove the polishing residues (particles) remaining on the surface of the substrate after polishing, the cleaning section has a plurality of cleaning modules for performing rough cleaning (primary cleaning) of the surface of the substrate and finish cleaning (secondary cleaning) of the surface of the substrate. The polished substrate is transported by a transport robot or the like from the polishing unit of the polishing section to the cleaning modules of the cleaning section where the substrate is cleaned successively in the primary and secondary cleaning processes. After the substrate is cleaned, the substrate is returned to the loading/unloading section.
However, if a large amount of polishing residues (particles) are attached to the surface of the polished substrate that is transported by the transport robot or the like from the polishing unit of the polishing section to the cleaning module of the cleaning section, even in the cleaning module which performs rough cleaning of the surface of the substrate, the surface of the substrate may possibly be damaged by the particles, or the particles that have been removed may be reattached to the surface of the substrate during cleaning, so that the cleaning capability may deteriorate. In addition, if dirt and dust are attached to the surface of the substrate while the substrate is transported to the polishing unit, the polishing capability of the polishing unit tends to be lowered.
The applicant of the present invention has proposed a polishing apparatus which ejects a cleaning liquid to a top ring located at a substrate transfer position to clean the lower surface of the top ring and the like as disclosed in Japanese laid-open patent publication No. H9-254017. There have also been proposed a planar polishing apparatus which ejects a cleaning liquid toward a polished workpiece held by a block while the polished workpiece is transported, thereby quickly cleaning the polished workpiece as disclosed in Japanese laid-open patent publication No. S62-224563, and a polishing head cleaning apparatus which ejects a cleaning liquid from a cleaning nozzle at a desired angle to a lower surface of a polishing head to clean and remove residual deposits from a retainer ring at the reverse side of the polishing head and a contact area which has contacted the rear surface of the wafer as disclosed in Japanese laid-open patent publication No. 2008-272902.
In order to prevent a substrate with a large amount of polishing residues attached thereto from being introduced into the cleaning module and also to prevent the substrate to which dirt and dust is attached in the middle of its delivery from being introduced into the polishing unit, it is necessary to clean the substrate held by the top ring together with the top ring. It has been customary to eject a cleaning liquid from a cleaning nozzle disposed at a substrate transfer position toward the lower surface of the top ring located at the substrate transfer position, thereby cleaning the substrate held by the top ring together with the lower surface of the top ring.
A mechanism for transferring substrates is provided at the substrate transfer position, and thus it is difficult to place the cleaning nozzle in a position suitable for cleaning the substrate, in the vicinity of the substrate held by the top ring that is located at the substrate transfer position. Consequently, the cleaning liquid cannot be ejected from an optimum position toward the substrate or a desired position of the lower surface of the top ring, and thus a sufficient cleaning capability cannot be obtained.
The apparatuses disclosed in laid-open Japanese patent publication No. H9-254017 and Japanese laid-open patent publication No. 2008-272902 are not configured to clean the substrate held on the lower surface of the top ring together with the lower surface of the top ring. The apparatus disclosed in Japanese laid-open patent publication No. S62-224563 is configured to eject the cleaning liquid toward the polished workpiece that is being transported, and does not take into account anything about cleaning the lower surface of the block that holds the workpiece.